In the last decades, various processes have been proposed for making absorbent cores with fibers and/or superabsorbent polymer particles (SAP particles), also referred to as absorbent gelling polymer particles (AGM particles), including processes whereby said material is laid down on a moving surface, such as a drum surface with one or more reservoirs and held onto said surface by for example vacuum. These approaches include indirect printing methods whereby the AGM and/or fibers are taken up by a drum from one or more bulk storage(s) of said fibers and/or AGM particles, and whereby the drum then rotates towards a substrate such as a nonwoven, to then release the AGM and/or fibers onto the substrate. The drum may have one or more reservoirs, each being in the shape of a structure such as for example an absorbent (diaper) core, which is then filled with fibers and/or AGM. However, at high speed, such complete structures are difficult to transfer completely and/or accurately at high speed onto a second surface, such as a moving nonwoven web. In more recent years, it has been proposed to deposit fibers and/or AGM into smaller reservoirs. Such a multitude of smaller reservoirs may then together be in the form of a diaper core, so that when the AGM content of all the reservoirs is transferred onto a second surface, like a nonwoven web, a core is formed. This is for example described in EP-A-1621165. With such s method and apparatus an improved transfer of the solid material can be achieved; furthermore, such an apparatus and process may be used to produce absorbent cores that have a specific profile or distribution, such as a predetermined pattern, MD-, CD-, or thickness-profile, corresponding to the pattern/depth of the reservoirs. The AGM or fibers may be retained on the drum surface, in the reservoirs, by use of vacuum suction under the surface. The AGM or fibers may be removed from the drum by use of gravity, or optionally, by use of additional blow-off air, to blow the solid material of the drum surface.
The inventors found that, depending on the apparatus and process characteristics or depending on the requirements of the structures to be produced, such proposed (indirect) printing or transfer processes do not always have the desired (complete) transfer or the complete and/or accurate release of the solid material, for example at high process speeds (of more than 800 or more than 1000 parts (e.g. structures, such as absorbent cores) per minute), or for example when fine particulate material is used, or for example when the moving surface (such as a print roll or drum) comprises substantial zones extending in machine direction, MD and cross-machine direction CD) without reservoirs (for example corresponding to the zones between absorbent cores of the web of absorbent cores produced by the method or with the apparatus). The inventors found that the air flow and/or vacuum suction may be impeded in some of such instances, or that the air flow and/or vacuum may be difficult to control in some instances.
The inventor now found a new method and a new apparatus that can provide an improved reception/transfer and/or release of solid material, resulting in a more consistent or accurate transfer or deposition of the solid material, e.g. on a substrate, and hence improved absorbent core formation, said method and apparatus being more flexible in use, e.g. at a wide span of process or apparatus settings characteristics, for example even at high speeds, or even when small reservoirs am used, or even when fine particulate material is transferred.